I have a generic struct that declares a method, and an extension to this struct that overloads the method in the case where the generic parameter conforms to Error. This has worked fine so far, but the Swift 5 compiler rejects this as an ambiguity error. It seems to be special-casing Error somehow because this doesn't happen with other protocols. This compiler error happens even in Swift 4 mode (though I don't believe it should happen in Swift 5 mode either).
This error means Xcode 10.2 cannot compile https://github.com/lilyball/Tomorrowland.